Due to the possibility of using WebGL to examine the contents of cross-origin images [1], it is necessary to disallow the use of cross-origin media in WebGL.
The WebGL specification and conformance suite have already been updated to mandate this new behavior, and the HTML specification and WebKit implementation have been updated to allow applications to use CORS to request permission to use cross-domain media.
[1] http://www.khronos.org/webgl/security/

I looked at the failures on the three affected platforms (Leopard, GTK and Qt) and the reason the new tests were failing there is that WebGL isn't supported on those ports. I'm recommitting the original patch with new Skipped entries for those three ports.